What would serve as a control group?

I'm doing an experiment to test the effect of a light's intensity on photosynthesis. I have one leaf under a normal light, one under a higher intensity light, and one under no light at all. But I need a control group. What could I use as a control group?|||the one leaf under a normal light--(natural conditions)





鈭傃斚壞?s蟽n蟽uchi 畏i !|||I don't understand why you need a control group? If this were a medication trial one group would get nothing as a control - in this case the plant with no light would be the control. One would get a placebo -and the other the real thing. That doesn't apply in this situation. I would like to make a suggestion - different types of light have an effect so make sure you are supplying the same type (incandescent or fluorescent or full spectrum) as your source. You could do this same thing in a sunny window - the plant furthest from the window would most likely grow poorly and the one in the closet would become long and spindly trying to get to any light. You could use 3 plants in natural light at varying distances as the control and then 2 more groups getting all fluorescent at different distances (intensities) from the source and another group getting incandescent light - why not throw another group getting full spectrum too.